loadgenerator: check curl install

without &&, load generator startup was failing intermittently when it fails
to install curl from apk-add.

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

kubernetes-manifests/loadgenerator.yaml

@@ -28,7 +28,7 @@ spec:
       initContainers:
       - name: wait-frontend
         image: alpine:3.6
-        command: ['sh', '-c', 'set -x;  apk add --no-cache curl; 
+        command: ['sh', '-c', 'set -x;  apk add --no-cache curl && 
           until timeout -t 2 curl -f "http://${FRONTEND_ADDR}"; do 
             echo "waiting for http://${FRONTEND_ADDR}"; 
             sleep 2;